1. Field of the Invention
The present invention relates to a lens apparatus and an image pickup system.
2. Description of the Related Art
According to one known lens interchangeable type camera system, a camera body has an autofocus (“AF”) function and a focus preset function (“FP”) configured to move a focus lens to a stored position, and a lens apparatus includes a driver and a position detector of the focus lens. A current focus position (as a position of the focus lens) is transmitted from the lens apparatus to the camera body, and a target focus position or moving amount is transmitted from the camera body to the lens apparatus based upon it.
Japanese Patent Laid-Open No. (“JP”) 2008-227799 proposes a method for solving a change of a movable range of a focus lens with a zoom position in a rear focus lens. In the rear focus lens, as a zoom position (as a position of the zoom lens) is changed, a focus position shifts and it is necessary to move the focus position according to the zoom position so as to focus upon the same object distance. A relationship between the zoom position and the focus position is referred to as a “cam locus.”
However, due to an individual difference caused by a manufacturing error of each component, a temperature change, and an insertion/ejection states in/from the optical axis of a variety of filters, a relationship between the focus position and the object distance can be changed from the designed value or previous state information of the focus position. Since the performance and temperature of each component as well as an insertion/ejection (optical condition) of each filter affect the optical performance of the camera system, they may be referred to as an “optical characteristic” hereinafter. For example, the cam locus may shift from the designed value due to an individual difference, an optical characteristic at a position stored in the FP may differ from the current optical characteristic, and an optical characteristic in the scan used to detect the contrast peak position in the contrast AF may differ from the current optical characteristic. Then, none of the focus position of the designed value, the position stored in the FP function, and the focus position corresponding to a detected contrast peak position corresponds to a target object distance. JP 2008-227799 does not consider a focus shift caused by a change of the optical characteristic.